Sean Mercer, a gun-obsessed teenager, was today sentenced to a minimum of 22 years in prison after being found guilty of the murder of schoolboy Rhys Jones, one of Britain's youngest victims of gangland violence.

In sentencing Mercer, the judge Mr Justice Irwin said: "This offence arose from the stupid, brutal gang conflict which has struck this part of Liverpool. You were caught up in that from a young age, but it is clear you gloried in it. It is wrong to let anyone glorify or romanticise this king of gang conflict.

"You are not soldiers. You have no discipline, no training, no honour. You do not command respect. You may think you do, but that is because you cannot tell the difference between respect and fear. You are selfish, shallow criminals, remarkable only by the danger you pose to others."

The jury of seven women and five men unanimously convicted Mercer of murder after almost four days of deliberations. They reached their verdict yesterday but it could not be reported until this afternoon.

Mercer, 18, a member of the Crocky Young Guns gang, shot Rhys while he walked home from football practice in Croxteth, Liverpool, in August last year. He missed his intended victims – members of a rival gang who had gathered in a pub car park – and hit Rhys in the neck with a stray bullet. He died at the scene in the arms of his mother.

Fellow gang members James Yates, 20, and Nathan Quinn, 18, of Croxteth; Gary Kays, 26, and Melvin Coy, 25, of West Derby, Liverpool, and Boy M, 16, who cannot be named for legal reasons, were convicted unanimously of assisting an offender after they helped Mercer evade the police for months. Boy K, who can now be named as Dean Kelly, 17, of Croxteth, was also convicted today of four related charges.

Kays and Coy were both jailed for seven years for trying to help Mercer cover the crime after he went to Boy M's house. The rest of the gang will be sentenced at a later date.

At a press conference on the steps of Liverpool crown court, Rhys's father, Stephen Jones, said: "Finally justice has been done. It's not the final chapter, but now we can begin the challenge of rebuilding our lives.

Detective superintendent Dave Kelly, said: "Today Sean Mercer will be sentenced for the murder of Rhys Jones. Mercer's conduct showed total disregard for Rhys and others... he has shown no remorse whatsoever.

"I hope that this verdict will bring it home to him what he has done and the pain and suffering that he has caused."

As Mercer's guilty verdict was announced to the silent courtroom yesterday, Melanie Jones, 42, who was sitting opposite her son's killer, burst into tears and buried her head in her husband's shoulder to stifle her sobs.

Stephen Jones choked back tears as Mercer blinked, looked down and visibly paled, repeatedly puffing his cheeks out. For the first time in the trial, the teenage killer looked close to showing emotion as he stared towards the public gallery where his father sat, with tears rolling down his cheeks.

Mercer's father, Joseph McCormick was also in tears as the verdict was announced, and mouthed "I love you" to his son - and left the court.

But Quinn cracked a joke, inaudible behind the reinforced glass of the dock, and he and other defendants smiled and laughed. As they were all led away Mercer shook Quinn's hand and the pair hugged before they were led down to the cells.

After the shooting, Mercer cycled to the home of an acquaintance, Boy M, where he called on other gang members to help him avoid the law.

He was driven to a lock-up garage on an industrial estate where his clothes were burned and his body washed down with petrol, Liverpool crown court heard.

A key witness, known as Boy C, told the court Mercer gave him the suspected murder weapon, a Smith & Wesson .455 revolver, to hide.

The gun was found in the loft of the 17-year-old friend of Mercer. The boy was on holiday in Florida with his family and was arrested on his return. He later became a crucial witness in exchange for immunity from prosecution.

Mercer, of Croxteth and with a previous conviction for minor drug offences, was well-known in the community. In the aftermath of the killing, his name appeared on websites and local graffiti.

He was arrested days after the shooting, but it was not until eight months later that police had gathered sufficient evidence to charge him with murder.

Mercer denied murder and claimed he was at a friend's home watching a DVD when Rhys was killed.

What the jurors did not know during the trial was that just two months before he shot Rhys, Mercer was involved in an incident that presaged the killing.

Waving a gun, he rode a motorcycle past members of the public on rival gang territory. The incident was not reported to police at the time. The jurors were also unaware that just weeks after shooting Rhys, Mercer was given a three-year Asbo for terrorising security guards at a sports centre.

During the trial, the jury heard that Mercer was a leading member of the Croxteth Young Guns gang, which terrorised the local community and was involved in a long-running and bloody feud with the Strand Gang, based on the neighbouring Norris Green estate. Mercer had an "intense hatred" of Strand Gang member Wayne Brady. When told by Coy and Kays that Brady, 19, and two rivals others had been seen cycling near the Fir Tree Pub on Croxteth Crew territory, Mercer set about the murder.

Dressed in a black hoodie and tracksuit, Mercer got hold of Yates's Smith & Wesson .455 revolver and cycled to the pub where he took up position on a grass verge alongside the car park.

Standing astride the bicycle with his arms out-stretched in front of him, he clasped the gun with both hands and fired three shots at Brady's friends, moving his arms in an arc to follow their movements on their bicycles.

Rhys, distracted by the sound of the first bullet, which struck a shipping container in the car park, turned toward the gunman and was struck in the neck by the second bullet. Mercer then adjusted his position to aim one final shot at his two rivals. The third bullet struck a disused well as the gunman and his targets fled the scene.

Rhys was the star player of the Fir Tree under-12s football team and a season-ticket holder at Everton.

More than 2,500 mourners, many dressed in blue and red – the colours of Liverpool's Premier League teams – attended his funeral. He was buried in a blue coffin adorned with the badge of his beloved Everton.